-LRB- CNN -RRB- -- One Australian gold prospector has hit pay dirt .

The man , described as an amateur explorer who wants to remain anonymous , unearthed a 5.5 kilogram golden nugget 60 centimeters in the ground outside Ballarat , a city about an hour and a half drive west of Melbourne .

Experts say the value of the find is at least $ 300,000 .

`` He came in to my shop at 12:30 p.m. on Wednesday and had a grin from ear to ear , '' Cordell Kent , owner of The Mining Exchange Gold Shop , told CNN . `` His eyes were sparkling . ''

The 47-year resident of Ballarat says that gold has been continuously found in the region since 1851 , but technology has recently become an essential aid for modern prospectors .

`` In the last 10 years it 's gotten very , very hard to find nuggets over a kilo , so this -LRB- 5.5 kilogram -RRB- one is extremely rare , '' says Kent . `` In the old days miners could only see or feel gold - but now with detectors they can hear it . ''

A Minelab GPX Model 5000 metal detector was used to find the nugget , Kent says . In Australia , the machine retails for nearly $ 7,000 , according to Gary Shmith , Minelab 's General Manager for the Asia Pacific .

Shmith expects collectors may already be eyeing a potential purchase of the Ballarat nugget because of its rarity .

`` My guess is that it would sell at 20 % or 30 % above its weight in gold . A nice , small nugget would already sell for 10 % to 15 % above its weight in gold . ''

Kent says the lucky prospector is back at work , `` detecting right as we speak . ''

`` He does n't want anyone to know his bit of ground . There are only four people who know that he found it -- he and his wife and me and my wife . And he 's hoping the one he found this week is a small piece and that there are bigger ones still out there . ''

While many people in the region have been searching for gold for decades , Kent 's friend only started last year .

Other prospectors - old and new - will hope that they will be as lucky .

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Amateur Australian prospector unearths 5.5 kilogram golden nugget

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Experts say value of gold nugget at least $ 300,000

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Gold first found around city of Ballarat in 1851